This invention relates to oil burners and more particularly to a vaporizing type oil burner adaptable for use in forced flue type kerosene space heaters for houshold use and other heating equipment.
Generally, in vaporizing type oil burners, the oil caused to flow on the bottom plate of a vaporizer pot is heated by the radiation heat of a flame in an upper portion of the vaporizer pot so as to vaporize the oil. At the time of initiation of combustion, an ignition heater is operated to ignite the oil caused to flow on the vaporizer pot bottom plate. The combustion of the oil thus ignited produces heat which causes the oil in other regions of the bottom plate to vaporize. The volume of oil thus vaporized gradually increases, and an increase in the volume of vaporized oil causes the position of combustion to gradually move upwardly. When the combustion has moved to a combustion compartment in an upper portion of the vaporizer pot and the volume of vaporized oil has stabilized, a state of steady state combustion is reached. Thus the burners can exhibit a predetermined heating performance.
Some advantages are associated with vaporizing type oil burners of the prior art. First of all, it takes a long time after ignition is taken place till steady state combustion is obtained, or their combustion rise time is long, so that they are often delayed in performing heating function to their full capacity. Secondly, it is impossible to obtain a compact size in a burner. Thirdly, severe tolerances are required for positioning the vaporizer pot bottom plate on a horizontal plane. If the vaporizer pot is positioned such that its bottom plate is inclined even slightly with respect to the horizontal combustion of the oil will take place on the lower portion of the bottom plate only and no combustion will occur on the higher portion thereof. Thus what is referred to as unbalanced combustion will take place in the vaporizer pot, with a result that lack of air supply and excess air supply will occur locally and incomplete combustion of the oil will ensue.
The reasons why oil burners of the prior art have the aforesaid disadvantages will be described in detail hereinafter. In regard to the long combustion rise time, it is known that this time depends greatly on the rate of increase in the volume of vaporized oil in relation to the time elapsing after initiation of combustion. Generally, the volume of vaporized oil in a vaporizer pot is related to the oil vaporizing area, the temperature of oil, the temperature and humidity of air for combustion fed to the interior of the vaporizer pot, the volume of oil fed to the vaporizer pot, or the like. When operation of the burner is started, the volume of supplied oil is generally equal to the volume of oil supplied to the vaporizer pot at the time of steady state combustion. The oil vaporizing surface is planar and the area thereof is equal to that of the bottom plate of the vaporizer pot.
For a little while after initiation of combustion, the temperature in the vaporizer pot is low and the volume of burned oil is small, so that the oil fed to the bottom plate of the vaporizer pot is low in temperature and the volume of vaporized oil is much smaller than when the oil burns in steady state combustion. Consequently, the volume of fed oil is greater than the volume of vaporized oil, and excess oil collects on the surface of the bottom plate to form an oil film thereon. Owing to an increase in the thermal capacity of the oil film, difficulty is encountered in accelerating the rise in the temperature of oil, and accordingly the rate of an increase in the volume of vaporized oil and the rate of an increase in the burned oil become small. Thus, it takes a long time before the state of steady state combustion is reached and hence the combustion rise time is long.
It is impossible to obtain a compact size in an oil burner for the reason that the area of the bottom plate of the vaporizer pot is the oil vaporization area at the time the operation of a burner is started, so that it is impossible to reduce this area. That is, if this area were reduced, the combustion rise time would become longer, and since the oil temperature does not rise at a stretch, the oil would undergo thermal decomposition and become tar-like. Thus the oil would not only burn in incomplete combustion but also take time before it burns satisfactorily to achieve stable heating effects.
The reason why severe tolerances are required for positioning the bottom plate of the vaporizer pot is as follows. If the bottom plate were tilting, the oil caused to flow thereon would collect in the lower portion of the bottom plate and would not flow to the higher portion thereof. Meanwhile the air for combustion is distributed such that it matches uniform spreading of the oil. Therefore, if unbalanced distribution of the oil occurred as aforesaid, there would arise the lack of air for combustion in the portion of the bottom plate on which the oil has collected. This would lead to unbalanced combustion of the oil due to the lack of air, so that soot would be produced and the stream of air current would be disturbed. This would further increase the tendency of incomplete combustion.